Field of the Invention
The invention relates to a method for controlling an electromechanical actuator, in particular, to an actuator for controlling an internal combustion engine.
An actuator is described in German Published, Non-Prosecuted Patent Application 195 26 683A1 corresponding to U.S. Pat. No. 5,691,680 to Schrey et al. The actuator has an actuating element in the form of an inlet and/or outlet valve, and an actuating drive. The actuating drive has two electromagnets between which, and, in each case against the force of a resetter, an armature plate can be moved by switching off the coil current to the holding electromagnet and switching on the coil current to the capturing electromagnet. The coil current to the respective capturing electromagnet is kept constant at a predetermined capture value I_MAX for a predetermined time period, is then switched off for a predetermined switched-off time, and is then regulated at a holding value by a two-point regulator with hysteresis. The time response of the coil current during the switched-off time is used to identify bouncing of the armature plate against the respective electromagnet, and to correct the capture value appropriately. However, the coil current cannot be set to the corrected capture value until the next capture process. Thus, the armature plate may move so far away from the capturing electromagnet during the switched-off time that the holding current can no longer apply sufficient force to move the armature plate into contact with the capturing electromagnet.
Another actuator is described in U.S. Pat. No. 5,650,909 to Remele et al. The actuator has an actuating element in the form of an injection valve, and an actuating drive. The actuating drive has an electromagnet, an armature, and a resetter. When current flows through a coil of the electromagnet, the armature plate can be moved against the force of the resetter into contact with the electromagnet. The actuating drive has an associated regulator, whose controlled variable is the current through the coil of the electromagnet. In order to move the armature from a first position to make contact with the electromagnet, a maximum value is predetermined as a set value of the current through the coil until the armature starts to move. An opening value is then predetermined as the set value, which is less than the maximum value. When the armature is in contact with the electromagnet, a holding value is predetermined as the set value, which is less than the opening value. Choosing the opening value to be low, as is advantageous in order to keep the power consumption low, may lead to the armature plate dropping and not coming into contact with the electromagnet.
European published, non-prosecuted patent application no. EP 07 24 067 A1, corresponding to U.S. Pat. No. 5,752,478 to Sono et al. and U.S. Pat. No. 5,765,514 to Sono et al., discloses another actuator having an actuating element in the form of an inlet and/or outlet valve. A position sensor is provided to detect the position of the inlet and/or outlet valve.